1. Field of the Invention
The present invention relates to laser sources having mode selection.
2. Discussion of the Background Art
In the optical communication industry there is a need for testing e.g. optical components and amplifiers with laser signals. For this purpose, various types of laser cavities are known.
Tunable lasers are described e.g. as the so-called Littman geometry in “Liu and Littman, Novel geometry for single-mode scanning of tunable lasers, Optical Society of America, 1981”, or as the so-called Littrow geometry in EP-A-952643 or U.S. Pat. No. 5,802,085. Bragg-reflector type cavities are shown e.g. in “A. Nahata et al., Widely Tunable Semiconductor Laser Using Dynamic Holographically-Defined Distributed Bragg Reflector, 2000 IEEE”.
The Littman cavity allows tuning wavelength and optical length of the cavity at the same time by changing only one parameter of the geometry, i.e. the tuning element. However, as already pointed out by Liu and Littman in the aforementioned document, mode hops might occur due to deviations of the real geometry with respect to the perfect Littman configuration. Fine adjustment e.g. of the laser end mirror is proposed to avoid mod hops. Examples of lasers, based on the Littman or other geometries, and various options for reducing or avoiding mode hops can be found e.g. in the co-pending European Patent applications 01121408.7, 01113372.5, or 01113371.7 of the same applicant, or in the pending International Patent application PCT/EP02/04736 also by the same applicant.